Adjustable dumbbell



FIG. 1 is a top, front, right side perspective view of an adjustable dumbbell, showing my new design;

FIG. 2 is a bottom, rear, left side perspective view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a left side elevational view thereof;

FIG. 6 is a right side elevational view thereof;

FIG. 7 is a top plan view thereof; and,

FIG. 8 is a bottom plan view thereof. 

CLAIM The ornamental design for an adjustable dumbbell, as shown and described. 